How is it that I’ve never heard of the game Battleship before this crossword?

Battleship (also Battleshipsor Sea Battle) is a guessing game for two players. It is known worldwide as a pencil and paper game which dates from World War I. It was published by various companies as a pad-and-pencil game in the 1930s, and was released as a plastic board game by Milton Bradley in 1967. ~ Wikipedia

BATTLESHIP(56A. Four units, in 56-Across)PATROL BOAT (18A. Two units, in 56-Across)SUBMARINE (23A. Three units in 56-Across)AIRCRAFT CARRIER (37A. Five units, in 56-Across)DESTROYER (49A. Three units, in 56-Across)